It is well known that monomers, dimers, trimers, oligomers and prepolymers which have unsaturated bonds in the molecule cause photo polymerization in a presence of a photo polymerization initiator. Further, this phenomenon has been widely utilized in photo polymerization type photo-polymers or photoresists used for producing printing plates, printed base plates or I.C., etc.
Useful photo polymerization initiators include various substances which have been found to be practical. For example, there are benzoin compounds such as benzoin, benzoin methyl ether, or benzoin ethyl ether, etc., carbonyl compounds such as benzil, benzophenone, acetophenone or Michler's ketone, etc., azo compounds such as azobisisobutyronitrile or azodibenzoyl, etc., sulfur compounds such as dibenzothiazolyl sulfide or tetraethylthiuram disulfide, etc., halogen compounds such as carbon tetrabromide or tribromophenyl sulfone, etc., and 1,2-benzanthraquinone, etc.
However, these photo polymerization initiators are not sufficiently satisfactory. When they are used for polymerization of various ethylenically unsaturated compounds, they do not always have good sensitivity as photo-polymers.
Further, in recent years, methods of forming images with laser have been examined. There has already been some practical application in the field of laser direct plate making in the production of printing plates, laser facsimile and holography, etc. Light-sensitive materials for laser used in such cases include silver salt light-sensitive materials, electrophotographic materials, photochromic materials and photo-polymers, etc. The photo-polymers have a very low sensitivity as compared with silver salt light-sensitive materials and electrophotographic materials, and, further, their sensitive wavelength range is from ultraviolet to ultrashort visible rays. For example, when monochromatic light of Ar.sup.+ laser having the wavelength of 488 nm is used, the silver salt film (Kodalithortho Film 2556 type 3) requires an energy amount of 0.0205 mJ/cm.sup.2, while the photo-polymer (Kodak polymatic Lithoplate LN-L) requires an energy amount of 7,000 mJ/cm.sup.2. Further, if ultraviolet rays of the wavelength 351/364 nm are used, the photo-polymer requires an energy amount of 100 mJ/cm.sup.2.
As described above, the prior photo-polymers are not satisfactory with respect to both sensitivity and their sensitive wavelength range, and they are, particularly, unsuitable as light-sensitive materials for visible light laser.